More than the sun: getting the most from solar energy storage with field data | Science| In-depth reporting on science and technology | DW | 05.08.2014
  1. Inhalt
  2. Navigation
  3. Weitere Inhalte
  4. Metanavigation
  5. Suche
  6. Choose from 30 Languages


More than the sun: getting the most from solar energy storage with field data

Germany's biggest, and newest, solar storage park is also an open-air solar laboratory. The idea is to use real-time data from the field to make forecasting ultra-accurate.

Solar power plants sit well with the German love of order - they usually consist of row upon orderly row of identical solar panels, all tilted at exactly the same angle and facing in exactly the same direction.

But the country's biggest solar storage park breaks with this perceived tradition.

Located at the Karlsruhe Institute of Technology (KIT), the solar storage park hosts more than a hundred arrays of mounted solar panels that look like they have been scattered randomly around the grassy field by some kind of mad scientist.

The modules slope off at unexpected angles. There's not a straight row in sight.

Method in the madness

The solar park is part of a KIT research project collecting data on various combinations of modules, inverters (which convert the DC current produced from the panels to the AC current used by most households), inclinations and orientations.

Photovoltaic (PV) panels are usually mounted at an angle of around 30 degrees in northern Europe.

In theory, the 30 degree angle optimizes the energy produced by the solar panels over the course of a year.

In practice, however, scientists say they see things under real conditions that don't appear in their simulations - such as the dust and dirt which collect on the solar modules and diminish the amount of power they produce.

"And how well rain cleans the surface depends on the inclination of the solar modules, so when you measure [performance], you find deviations from the theory," explains Olaf Wollersheim, a physicist and head of KIT's Competence E project, which is conducting research into electric storage systems.

The KIT research group is collecting data on 54 different slope angles at the solar park.

Solar Storage Park KIT

The KIT solar storage park should break even at about the same time the panels will need replacing

As for testing different orientations, there's good reason for that too.

Designed by law

In Germany, as elsewhere in the northern hemisphere, photovoltaic plants are usually built facing due south so they produce as much energy as possible.

Maximizing the energy harvest in this way was a logical consequence of Germany's Erneuerbare-Energien-Gesetz (renewable energy act), which forces utility companies to pay an above-market rate for solar power fed into the national power grid. As a result, Germany's solar producers could turn more of a profit by selling their solar power and covering their power needs by buying power from the grid.

But the situation is changing.

The feed-in tariff has sharply declined, and the cost of buying energy from the grid has increased.

So it now makes more sense for solar power producers to consume their own energy.

Unfortunately for those who might want to use the photovoltaic power they produce, one of the shortfalls of solar is that PV energy is produced in the middle of the day when many people aren't at home - which is where the research into various orientations comes in.

New orientations

If power can be produced when it's most needed, it can reduce the amount of battery storage the system needs.

"If, for instance, you like to use a coffee machine in the morning, it's no good having the PV producing your energy at noon or in the evening," says Wollersheim. "But if you have modules facing east, you can catch the early morning sun and therefore directly consume some of the PV energy for your household [when you need it]."

Solar Impulse 2

Storage is the key: the Solar Impulse 2 can fly day and night on solar power

Wollersheim walks over to a container in the middle of the field and unlocks the door to expose two racks of batteries.

Each rack is equipped with eight different modules containing lithium ion batteries with a capacity of 48 kW-hours. They are the same as the batteries found in electric cars.

The E-Competence group has conducted research into all types of commercially available battery technology. Wollersheim says the lithium ion batteries are the best option, based "cost and performance," for this type of storage application.

"They last several thousand cycles of charging and discharging, and thanks to the automotive industry they are available at relatively low prices already," he says.

The researchers collect performance data every second from the 102 solar tables in their test field. It's only been online since July 2014, so the data has just started flowing. But in the long term it's hoped the numbers will show how the various components work and age under real conditions.

"We will have a really nice online tool where you can see immediately how much energy is produced by each module and how much current you get from which inverter," says KIT scientist, Nina Munzke.

Having real-time data collected under real conditions will allow the scientists to test simulations and possibly result in more accurate forecasting, which is essential for making solar systems more reliable.

"Your software has to be able to forecast how much solar energy will be available during the day and how much energy will be needed during the day," Munzke says.

But this solar storage plant isn't just a research facility.

The solar energy produced here is fed into KIT's own network, saving the university around 70,000 euros a year in power bills. This means the initial 1.5 million euro cost of the plant should be paid back over the next twenty years - the estimated life of the photovoltaic facility.

DW recommends

WWW links

Audios and videos on the topic